As the use of wireless electrical devices become more prevalent in both business and personal environments, the guidelines and restrictions related to the usage of these devices are continuously examined by regulatory bodies, such as the Federal Communication Commission (“FCC”). These regulatory bodies have taken measures to ensure that people with hearing impairments may have access to communication networks through digital wireless telephones. Thus, the FCC enacted the Hearing Aid Compatibility Act of 1988 (HAC Act) to ensure that all telephones manufactured or imported for use in the United States, and all “essential telephones” are hearing aid-compatible. The collection of “essential telephones” had been defined to include coin-operated telephones, telephones provided for emergency use, and any other telephones frequently needed for use by a hearing impaired person, such as telephones in the workplace, in hospitals and nursing homes, and in hotel rooms. Initially, wireless telephones were exempt.
While analog wireless telephones do not usually cause interference with hearing aid devices, digital wireless telephones may cause interference due to the electromagnetic energy emitted from the telephone's antenna, backlight, battery, and/or other components. In 2001, the FCC established a measurement standard for categorizing both hearing aid device and wireless devices in order to provide hearing-impaired individuals with access to wireless communication networks. The wireless devices were tested for radio frequency (“RF”) emissions as well as other emissions (e.g., magnetic field (“H-field”) emissions, electric field (“E-field”) emissions), while the hear aid devices were tested for susceptibility to such emissions. Both the wireless devices and the hearing aid devices were assigned categories based on a combined performance rating in order to establish which hearing aids are compatible with which wireless device.
In 2003, the FCC removed the exemption for wireless telephones from the original HAC Act. A timetable for compliance was established, wherein wireless service providers were required to offer customers access to predefined percentages of headsets that met certain RF, E-field, and H-field emission requirements. The predefined percentages have been gradually increased, such that by Feb. 2008, the service providers must ensure that 50% of their wireless headsets meet the emission requirements. Accordingly, the new HAC Act requirements can make compliance very expensive and difficult, if not impossible, with any electronic devices used near an individual's ears.
In the prior art, the field cancellation is made in the far field using a planar field model. However, due to the relative proximity of the transmitter and probes to an earpiece and the user's head (i.e., within less than ¼ wavelength), significant field distortion occurs in these areas. Furthermore, in this environment, a simple planar model of field strength is highly inaccurate.